Patent GB-804683-A (GB)
Title: Polyester resin and electrical conductors coated therewith
IPC: H01B3/42
Filed: 1957-03-28
Abstract: A polyester resin is the reaction product of (a) a mono-, di- or tri-alkoxybenzene dicarboxylic acid; (b) a dihydric alcohol and/or a fatty acid; and (c) a polyhydric alcohol containing at least three hydroxyl groups.  The dihydric alcohol may be a straight or branched chain polymethylene glycol of formula HOCaH2aOH, where a is 2-10 or diethylene, triethylene or dipropylene glycol.  The polyhydric alcohol may be glycerol, pentaerythritol, 1,1,1-trimethylol ethane or propane, diglycerol, dipentaerythritol or sorbitol.  The fatty acid may be that of a drying, semi-drying or non-drying fatty oil (many specified).  The polyesterification mixture preferably contains 1-6 hydroxyl groups per carboxyl group and 0.1-7.0 equivalents of polyhydric alcohol per equivalent of dihydric alcohol. Polyesterification is generally effected at 50-250 DEG  C. preferably in the absence of a solvent, although a solvent (e.g. xylene, toluene or petroleum fractions boiling above 250 DEG  C.) may be used. Polyesterification catalysts specified are lead oxide, lead acetate, zinc oxide, cadmium acetate, cuprous acetate, zinc acetate, magnesium acetate, beryllium acetate, stannic acetate, ferric acetate or nickel acetate.  At the end of the polyesterification free alcohols and any other volatile materials are desirably removed by heating the polyester at 250-300 DEG  C., preferably at subatmospheric pressure. The polyesters when dissolved in a solvent (e.g. cresol, xylenol, polyhydroxybenzenes, polyalkylbenzenes, petroleum hydrocarbons, ethyl acetate or methyl ethyl ketone) are especially useful as an insulating coating for magnet wires (see Groups XXXVI) but may also be used for coating wood or metal or as adhesives, the coating being heated to remove solvent and to further polymerize the resin.  The heating time may be reduced by including an esterification catalyst in the solution (e.g. one of those previously mentioned or zinc or cobalt octoate).  The polyester may be used in combination with other synthetic resins, e.g. silicone, melamineformaldehyde, epoxide, phenol-formaldehyde, aniline-formaldehyde, urea-formaldehyde, cellulose acetate, polyamide, vinyl, ethylene or styrene resins.  In examples: (1), (2), (3) and (5) a polyester was made by reacting ethylene glycol, glycerol and 5-methoxyisophthalic, 4-methoxyisophthalic or 4-methoxyphthalic acids.  (6) A polyester was made by reacting ethylene glycol, 1.1.1-trimethylol ethane and methoxyterephthalic acid.  (7) A polyester was made by reacting glycerol, 4-methoxyisophthalic acid and soya fatty acids; a varnish was made comprising the polyester, cobalt octoate, lead naphthenate, xylene and methyl ethyl ketone and a coating composition was made by adding titanium dioxide to this varnish.ALSO:Mono-, di- and tri-alkoxybenzene dicarboxylic acids in which the alkoxy group may contain 1-10 carbon atoms are used in the manufacture of alkyd resins (see Group IV (a)) and the Specification describes the following preparations: (1) 5-methoxyisophthalic acid is made by reacting dimethyl sulphate with 3,5-dimethyl phenol in presence of sodium hydroxide solution to form 3.5-dimethylanisole and oxidizing this with potassium permanganate dissolved in sodium hydroxide solution to the salt of 5-methoxyisophthalic acid which is then acidified with sulphuric acid.  (2) 4-Methoxyisophthalic acid is similarly prepared from 2.4-dimethyl phenol via 2.4-dimethyl anisole.  (3) 4-Methoxyphthalic acid is similarly prepared from 3.4-dimethyl phenol via 3.4-dimethyl anisole.  (6) Methoxyterephthalic acid is similarly prepared from 2.5-dimethyl phenol via 2.5-dimethyl anisole.